Bone bed drilling is a time consuming task during implant surgery, in part because of the precision required to ensure a good fit between the implant and the bone surface. The surface of the bone bed to which an implant is attached needs to be smooth and flat, in order to minimize complications such as biofilm formation in interstices between the surface of the bone and the surface of the implant if the bone surface is uneven, or inadvertent relocation of the implant after surgery due to poor contact adhesion if the bone surface is not flat enough.
For an implant that is affixed to a patient's skull these problems are particularly acute since the surface of the skull is curved, yet the surface of an implant is flat. So if an implant is placed directly on to the surface of the skull, it can rock because it is flat relative to the curved section of skull. The surgeon therefore needs to plane away a flat surface of the bone to accommodate the implant in a rigid manner. Additionally, the surface of the recessed portion needs to be as smooth as possible so that the area of contact with the implant is maximized over the recessed region and the implant does not wobble due to unevenness of the surface, and there are no cavities between the bone surface and the adjacent implant surface.
In many types of implant such as auditory prostheses, the portion of the implant that is in direct contact with the bone is a receiver/stimulator unit: if this item does not have good contact with the bone at all points on its surface, it can shift its position after surgery, leading to a degradation or variability in its performance, and a continual need to recalibrate it. Furthermore, cavities, if present underneath the receiver/stimulator, can lead to biofilm formation and higher infection risks for the subject, in the post-surgical phase. Biofilm formation is encouraged when there is a pocket of air between the implant and the bone, in which bacteria can grow. Such bacteria can spread and make an increased area of infection, thereby having a harmful impact on the implant recipient. There can be a similar propensity for biofilm formation in any imperfections that may exist on the edges of the bone bed: it is important that the side walls of the drilled out area are perpendicular to the flat area which was drilled out and this may not be easy to gauge.
Other methods for reducing biofilm include coating the surface of the implant with an anti-bacterial substance, or a material such as a silicone that fills the voids when the implant is affixed, as well as by designing the implant so that it has smooth surfaces. These approaches, however, do not address the goodness of fit of the implant.
Some implants have used a hydroxyapatite cement to affix it but the substance expands on setting and so is less desirable when the implant must fit snugly in the bone bed. Other ways of fixing an implant are by using a titanium bridge, or a suture above the implant, but these methods do not necessarily work well for all types of implant and may not address the issue of biofilm formation.
Many implant kits are provided with a surgical kit containing various implant templates that can be used by surgeons to check the depth, shape, and flatness of the bone bed during drilling and prior to attachment of the implant. Some examples are produced by Cochlear, Limited (e.g., the CI24RE implant template). In many instances, more than one template is required for the same implant because, the same template cannot necessarily be used to define the perimeter of the area before any drilling is done as the template that is used to gauge the proper depth of the recessed area.
FIGS. 1A, 1B, 1C, and 1D show the actuator 101 of an exemplary acoustic implant, its fixation system 111, its position in situ on a patient's skull 103, and a template 121 to assist the surgeon in drilling a recessed area of bone in which to position fixation system 111, and the corresponding receiver/stimulator 141. In this example, fixation system 111 is used to hold actuator 101 in the mastoid (bone behind the recipient's ear), as shown in FIG. 1B, and as further described herein. The receiver/stimulator unit that communicates with actuator 101 is not shown in FIGS. 1A-1C.
However, while implant templates do help a surgeon to create a flat surface by trial and error, they do not make it clear to the surgeon where to flatten the bone, or improve the perpendicularity of the sides of the bone bed, during surgery. Therefore, during bone bed drilling, surgeons often struggle to create a flat surface, and may end up unnecessarily drilling away additional bone at the wrong spots.
In the absence of any other way in the art to address the foregoing problems, there is accordingly a need for a method and device for facilitating reliable placement of a bone implant, in order to improve the efficiency of the surgical process, as well as ensure a greater fidelity of the implant's attachment to the bone surface.
The discussion of the background herein is included to explain the context of the technology. This is not to be taken as an admission that any of the material referred to was published, known, or part of the common general knowledge as at the priority date of any of the claims found appended hereto.
Throughout the description and claims of the application the word “comprise” and variations thereof, such as “comprising” and “comprises”, is not intended to exclude other additives, components, integers or steps.